A number of different air interfaces or radio access technologies have been developed and deployed via radio access networks in wireless communication systems to facilitate the provision of wireless communication services to users. These include, for example, wide area access networks, such as the GSM Radio Access Network (GRAN) of a GSM communication system, a GSM EDGE Radio Access Network (GERAN) of an EDGE enhanced GSM communication system, a UMTS RAN (UTRAN) of a UMTS communication system, an Evolved UTRAN (E-UTRAN) of a Long Term Evolution (LTE) system, and other radio access networks based on Wideband Code Division Multiple Access (WCDMA) technology and wireless access networks, such as wireless LAN (WLAN), Worldwide Interoperability for Microwave Access (WiMax) based networks and Wi-Fi based networks.
Communication devices that can support different radio access technologies, and so can communicate with different access networks, have also been developed. Such devices are sometimes called multi-mode devices. Such multi-mode devices may typically include several radio interfaces with each radio interface supporting a particular radio access technology.
When multi-mode communication devices are located in overlapping coverage areas of different access networks, it is possible to transfer communication between the different access networks of the communication systems. Typically, multi-mode communication devices that are capable of operating with multiple communication systems will have a preferred communication system out of the multiple communication system. The preferred communication system may be determined according to parameters, such as, what services are available on each of the communication systems, cost of services, Quality of Service (QoS), network identification and potentially user preference.
For example, a communication device, which is capable of communicating with a wide area network (such as a UTRAN of a UMTS communication system) and a WLAN and which is currently active and communicating via the UTRAN to access an external data network (e.g. a server connected to the internet), communicates with the external data network via a radio communication link with a base station of the coverage area or cell within which the communication device is situated currently. In UMTS, the base stations, which are part of the UTRAN, are known as Node Bs and a communication device is known as User Equipment (UE). If the UE moves into a coverage area of the WLAN communication system, normally the UE would handover to the WLAN as the preferred communication system: for example, to reduce battery consumption in the UE compared to communicating via the UTRAN.
The typical method to conduct a handover from a UTRAN to WLAN requires the UE to operate both the UTRAN and the WLAN radio interfaces simultaneously during the handover procedure. This is required because otherwise the handover latency would be too large. Thus, in the example given above, the UE performs a handover by activating the WLAN radio interface while the UTRAN radio interface is concurrently used for data communications with the server connected to the internet and executes a WLAN access control process and IP address allocation with Dynamic Host Configuration Protocol (DHCP). The WLAN access control process includes authentication and authorization procedures performed by an Authentication, Authorization and Accounting (AAA) server in the core network, and is typically time-consuming, especially when the UE is roaming when the HOME AAA server is required to authenticate the UE via a visited AAA server/proxy. The WLAN access control process involves communications between the WLAN radio interface of the UE and the WLAN and the WLAN and the AAA server. Once the WLAN access control process has been successfully completed (e.g. the UE is authenticated and authorised to access the WLAN), the UE releases the TCP connection with the server over the UTRAN radio interface and establishes a new TCP connection over the WLAN interface. Subsequently, communication with the server connected to the internet resumes.
If this handover procedure takes place when no data exchange is ongoing between the UE and the server, then normally no issues exist. If, however, the handover takes place during communication between the UE and the server, such as for example during an ongoing photo download, the communication (e.g. download) will be interrupted when the old TCP connection (over the UTRAN) is closed. When the new TCP connection is established, the previous communication will have to be restarted. For example, the UE will have to request again the same photo and the download will start from the very beginning. This makes the handover very inefficient since the original photo download cannot be resumed.
A mobility solution has been standardized by 3GPP in Technical Specification TS 23.327 in order to address this inefficiency. This is shown in FIG. 1. A home agent 102 is introduced in the 3GPP core network 100 to hide the mobility of the UE 101 from the server 104 connected to the external data network 106 (e.g. the internet) so the above issue data communication (e.g. photo download) interruption and restart does not occur. However, the UE 101 is still required to operate simultaneously the wide-area (e.g. UTRAN) and the WLAN radio interfaces because of the time required to perform the WLAN access control process via the AAA server 110. Some UEs cannot support simultaneous communications due to device limitations. For those UEs that can support simultaneous communications, co-existence issues between the different radio interfaces, such as high adjacent channel interference and high specific absorption rate (SAR), may arise. In addition, the UE 101 is required to implement Dual Stack Mobile IPv6 (DSMIPv6) protocol for mobility control and to setup a Virtual Private Network (VPN) with the Packet Data Gateway (PDG) 108 to cipher and integrity-protect the data communication. This is all very demanding and power consuming for the UE 101.